Abstract This competing renewal builds on successful completion of a double blind randomized controlled trial (RCT) of DHA supplementation during pregnancy in Cuernavaca, Mexico, and is a collaborative effort between the Hubert Department of Global Health, Emory University in Atlanta GA and the National Institute of Public Health (INSP) in Cuernavaca, Mexico. The overall objective is to extend to age 5 y our examination of the effects on the offspring of maternal supplementation during pregnancy with docosahexaenoic acid (DHA). Our central hypothesis is that DHA supplementation during pregnancy will improve early childhood development. In the original trial, 1094 pregnant women were randomized to receive daily a supplement of 400 mg of DHA or a placebo from 18-22 weeks of pregnancy. The 973 live births are currently being followed up to age 18 mos for measures of growth and development. We propose to study the birth cohort at age 5 y. We plan to collect a comprehensive set of measures of early childhood development (ECD) that are known to predict later intellectual functioning. The primary outcomes include global motor and mental development, executive functioning, specifically attention and memory, and inhibitory processes. Additional data on dietary intakes, health and exposure to early childhood stimulation both at the home and outside will also be obtained. All measurements will be obtained by a well trained and experienced field team; many team members participated in the parent study and have developed good rapport with the study population. We expect to recruit at least 85% of the eligible birth cohort and will have adequate power to detect effect sizes of 0.3 S.D. We will link these new data to our extraordinarily rich array of data that we collected prenatally, at birth, and at ages 1, 3, 6, 9, 12 and 18 mos. In addition to analyses that focus on the overall impact of supplementation with DHA, we will explore hypotheses concerning developmental trajectories. These data will also position us to continue to follow this cohort during their early school years.